Methods and systems for identifying material composition of objects

ABSTRACT

A method for identifying a composition material of an object located in an environment surrounding at least one device, in which at least one sensor is mounted on the device and communicates with at least one central processing unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a 35 U.S.C. § 371 National Stage of International Application No. PCT/EP2019/056842, filed Mar. 19, 2019, which claims priority to U.S. Provisional Patent Application No. No. 62/644,746 filed Mar. 19, 2018 and U.S. Provisional Patent Application No. No. 62/745,370 filed Oct. 14, 2018, all of which are incorporated by reference in their entirety herein for all purposes.

BACKGROUND

The disclosure relates to methods and systems for identifying material composition of objects in a 3-dimensional (3D) volume or space.

The disclosure also relates to the field of tridimensional sensors that are mounted on a device, such as a vehicle.

Providing a device with sensors that are able to generate tridimensional point clouds of the surroundings of the device has many interesting applications.

The generated point clouds may for instance be used to map an area travelled by a vehicle.

The generated point clouds may also be used to assist or to automate the driving system of the vehicle.

Examples of applications for driving assistance are object detection to trigger collision warning or collision avoidance, but the sensors may also be used in a fully autonomous vehicle, in order to automate the driving system of the vehicle.

However, in many situations, it may be necessary to determine the type of objects the vehicle may detect or may collide with, in order to control the vehicle with an appropriate driving response.

As an example, the vehicle may operate differently if the detected object is a child inadvertently crossing a street or a trash bin that has been left on the road on the path of the vehicle. Depending on the circumstances, the vehicle may decide or not to avoid a collision.

In order to differentiate between two different objects, it can be necessary to know the material composition of these objects. In the case of a child, the detected material composition will likely be the fabrics of his clothes or his skin, whereas in the case of a trash bin, the material composition will be rigid metal or plastic for instance.

To this end, it is known to use sensors that can emit a physical signal at multiple optical wavelengths. The sensors can then receive the signal that is reflected by the object for these different wavelengths. From this reflectivity response, it is possible to identify the material composition of the object by comparing the received reflectivity response with a database comprising reference reflectivity responses for known materials.

This however requires being able to compute the information received in real time, so that the appropriate command of the vehicle can be taken immediately or shortly after the object has been detected, and more particularly while the vehicle is moving.

Some prior art systems operate by emitting simultaneously at multiple optical wavelengths and by receiving successively the reflected response at different wavelengths.

However, such systems are too slow to be used in dynamic environments. Besides, if the vehicle is moving, each wavelength is received according to a different location of the receiver, and it becomes too complicated to aggregate the reflected signals as the number of wavelengths increases.

As another variant, some systems comprise a single emitter that can emit simultaneously at multiple wavelengths and a plurality of receivers, each receiver being configured to receive one reflected physical signal at a specific wavelength. In this way, the receivers when taken altogether can receive simultaneously the reflected signals for all the different emitted wavelengths.

However, such systems are complex since they require a large number of receivers. Besides, to perform effectively, the emitter and receivers must be aligned and positioned with a high degree of accuracy with regard to the vehicle. If one of the emitter or the receivers is inadvertently misaligned, the signal that is received may not be accurate and the vehicle may be unaware of a serious risk situation.

Besides, having several receivers, each having a dedicated electronics, is a particularly costly solution.

Finally, each receiver is assigned to a specific wavelength or wavelength range. The system is therefore not easily adjustable, which makes it less flexible if other wavelengths have to be used in the future with the same receivers.

SUMMARY

The present disclosure aims at improving this situation.

The object of the present disclosure is to provide reflectivity response of an object at multiple optical wavelengths in real time.

It is proposed a method for identifying a composition material of an object located in an environment surrounding at least one device, in which at least one sensor is mounted on the device and communicates with at least one central processing unit, wherein:

/A/ the sensor generates a point cloud frame of a continuous stream by emitting a physical signal at a wavelength, wherein the point cloud frame comprises a set of data points, at least one data point comprising coordinates of the object in a local volume surrounding the sensor at time t_(j) in a local coordinate system of the sensor, said data point also comprising an intensity value of a reflected physical signal corresponding to the emitted physical signal once reflected on the object, /B/ the central processing unit receives the point cloud frame and determines the coordinates of each data point of the point cloud frame in a global coordinate system of the environment surrounding the device, the intensity value being associated with the coordinates of each data point in the global coordinate system, /C/ the central processing unit stores in a memory the coordinates of the object in the global coordinate system, steps /A/ to /C/ are repeated with the sensor or another sensor generating another point cloud frame by emitting another physical signal at another wavelength, at time t_(j+1) so that at least two intensity values are associated to coordinates of the object in the global coordinate system, /D/ the central processing unit determines a reflectivity response of the object from the at least two intensity values, and /E/ the central processing unit identifies the composition material of the object.

The following features, can be optionally implemented, separately or in combination one with the others:

The central processing unit determines the coordinates of each data point of the point cloud frame in the global coordinate system of the environment surrounding the device by:

-   comparing the point cloud frame with a global cumulated     tridimensional map of the environment to determine an aligned point     cloud frame in the global coordinate system, and -   updating the global cumulated tridimensional map by merging the     aligned point cloud frame with the global cumulated tridimensional     map.

The sensor comprises at least one emitter and at least one receiver, the emitter being configured to emit a physical signal and the receiver being configured to receive the emitted physical signal once reflected on the object.

The sensor comprises the emitter and the receiver as a single unit.

The central processing unit identifies the composition material of the object by comparing the reflectivity response determined at step /D/ with reference reflectivity responses of known materials stored in a library.

The wavelengths of the physical signals emitted for the point cloud frames are selected in a random manner.

The wavelengths of the physical signals emitted for the point cloud frames are selected in a predetermined order.

The device comprises a plurality of sensors, wherein the sensors can respectively generate a point cloud frame by emitting a physical signal at a wavelength comprised in different spectral domains.

The sensors all communicate wirelessly with the central processing unit.

A point cloud frame corresponds to a full scan of the local volume of the sensor.

The coordinates of the object in the local coordinate system of the sensor comprises two angular coordinates and one radial coordinate.

The radial coordinate corresponds to the distance from the sensor to the data point, the distance being computed by comparing timing of the emitted physical signal and the reflected physical signal.

Steps /A/ to /C/ are repeated at least four times, so that at least four intensity values are associated to coordinates of the object in the global coordinate system.

The physical signal is a laser signal.

The device is a vehicle able to move in the environment.

In another aspect, it is proposed a system for identifying the composition material of an object located in an environment surrounding at least one device, the system comprising:

-   a plurality of sensors configured to be mounted on said at least one     device, each sensor being configured to generate a continuous stream     of point cloud frames, in parallel and asynchronously with the other     sensors, by emitting a physical signal at a wavelength , wherein the     point cloud frame comprises a set of data points, each data point     comprising coordinates of the object in a local volume of the     environment surrounding the sensor at time t_(j) in a local     coordinate system of the sensor, each data point also comprising an     intensity value of a reflected physical signal corresponding to the     emitted physical signal once reflected on the object, -   a central processing unit configured to communicate with each sensor     to continuously receive the continuous streams from the sensors,     determine the coordinates of each data point of the point cloud     frame in a global coordinate system of the environment surrounding     the device, and store in a memory the intensity value and the     coordinates in the global coordinate system, the central processing     unit being configured to determine a reflectivity response of the     object from the intensity values and to identify the composition     material of the object.

In another aspect, it is proposed an autonomous or semi-autonomous vehicle comprising a system according to the disclosure.

In another aspect, it is proposed a non-transitory computer readable storage medium, having stored thereon a computer program comprising program instructions, the computer program being loadable into a central processing unit of a system according to the disclosure and configured to cause the central processing unit to carry out the steps of a method according to the disclosure, when the computer program is run by the central processing unit.

Other features, details and advantages will be shown in the following detailed description and on the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a vehicle in an environment comprising several objects according to an embodiment of the disclosure.

FIG. 2 is a schematic top view of the vehicle of FIG. 1,

FIG. 3 is a schematic view of a system of the vehicle of FIG. 1 and FIG. 2 for identifying the material composition of an object located in the environment of the vehicle.

FIG. 4 is a graphic representation of a full scan of a local volume of a sensor of the vehicle of FIG. 1 and FIG. 2 at several different wavelengths.

FIG. 5 is a graphic representation of the reflected signals received for each physical signal emitted at several different wavelengths, the reflected signals being aggregate to obtain a reflectivity response of an object.

FIG. 6 is a flowchart showing a method for dynamically identifying a material composition of an object in the environment of the vehicle according to an embodiment of the disclosure.

DETAILED DESCRIPTION

Figures and the following detailed description contain, essentially, some exact elements. They can be used to enhance understanding the disclosure and, also, to define the disclosure if necessary.

Vehicle

The disclosure relates to a device. The device is advantageously movable in an environment E. The device can be any type of device, such as a handheld device, or it can be mounted on a relatively bigger element.

According to an embodiment, the device can be hand-carried by a person for instance.

According to another particular and non-limitative embodiment detailed below, the device is a vehicle 1 in an environment E.

The vehicle can be any type of vehicle configured to move in the environment E. Vehicles includes motor vehicles (motorcycles, cars, trucks, and buses), railed vehicles (trains, trams), watercraft (ships, boats), amphibious vehicles (screw-propelled vehicle, hovercraft), aircraft (airplanes, helicopters, drones) and spacecraft.

More particularly, FIG. 1 and FIG. 2 illustrate a vehicle 1 according to one embodiment of the disclosure.

The vehicle 1 is a wheeled vehicle whose direction can be controlled to follow a specific path P. It should be noted that the disclosure can be applied to a wide range of wheeled vehicles, rear-wheel-steering car, trucks, motorcycles and the like.

As illustrated on FIG. 1, the vehicle 1 is provided with a body 2, bearing at least one wheel 3, which delimits an inside of the vehicle from the environment E of the vehicle 1.

Sensor

The vehicle 1 comprises a system 10 for identifying a material composition of an object 20 located in the environment E of the vehicle 1.

The system 10 comprises at least one sensor 11. Advantageously, the system 10 comprises a plurality of sensors 11 a, 11 b, 11 c that are mounted on or inside the body 2 of the vehicle 1.

For instance, the vehicle 1 may be provided with three sensors 11 a, 11 b, 11 c respectively mounted on the back, on the top and the front of the vehicle 1, as illustrated on FIG. 1. However, the vehicle 1 may comprise only two sensors 11 or a higher number of sensors 11.

Each sensor 11 generates a continuous stream of point cloud frames of a local volume L_(j) surrounding the sensor 11.

By “point cloud frame”, it is understood a frame generated at a specific time, or during a short interval of acquisition.

By “continuous stream of point cloud frames”, it is understood a succession of point cloud frames, periodically generated or not, organized in a stream of data.

For instance, the sensor 11 is able to periodically generate point cloud frames with a given framerate of the continuous stream. The framerate can be equal or higher than 20 Hz (Hertz). The framerate can also be lower, for instance lower than 20 Hz, even lower than 10 Hz, or even lower than 5 Hz.

In the specification below, a point cloud frame generated by a sensor 11 is referred to as PCF_(j), the time of acquisition of this point cloud frame PCF_(j) is referred as t_(j) and a local volume L_(j) of the sensor 11 at said time t_(j) is referred as L_(j). In these references, the subscript j is the index of the frame in the continuous stream ST, j increasing over time with each newly generated frame.

The point cloud frames PCF_(j) can also be generated in parallel and asynchronously with other point cloud frames from other sensors 11.

By “in parallel and asynchronously”, it is understood that the sensors 11 are in general unaware of each other and the generation of point cloud frames PCF_(j) by the sensors 11 are not specifically synchronized together.

Thus, point cloud frames PCF_(j)a, PCF_(j)b, PCF_(j)c of respective continuous streams STa, STb, STc of the sensors 11 a, 11 b, 11 c may be generated at different respective times t_(j)a, t_(j)b, t_(j)c.

Point cloud frame

Each point cloud frame PCF_(j) of a stream ST comprises a set of data points M_(i) in a local coordinate system LCS of the sensor 11. A data point M_(i) corresponds to a tridimensional portion, such as a voxel, of the local volume L_(j).

A point cloud frame can comprise a high number of data points, such as 10,000 or even 100,0000 data points, or even higher. The number of data points can vary, depending on the desired resolution when scanning the environment E of the vehicle 1 with the sensor 11. The number of data points of a point cloud frame may also vary according to the framerate that is used; it the framerate is high, the number of data points of a point cloud frame that is needed may be lower.

More precisely, a data point M_(i) can correspond to an object 20, or a part of an object 20, located in the environment E of the vehicle 1.

The local coordinate system LCS is a coordinate system related to the vehicle 1, and more particularly to the sensor 11, for instance with an origin point located at the sensor location. The local coordinate system LCS may be a cartesian, cylindrical or polar coordinate system.

Each data point M_(i) comprises three-dimensional coordinates (φ_(i),θ_(i),d_(i))_(LCS), in particular in the local coordinate system LCS of the sensor.

The coordinates (φ_(i),θ_(i),d_(i))_(LCS) are representative of the location of the data point M_(i) in the local volume L_(j) of the sensor 11 at time t_(j).

Each data point M_(i) also comprises an intensity value I_(i) associated with the coordinates (φ_(i),θ_(i),d_(i))_(LCS) of the data point M_(i).

The intensity value I_(i) is representative of a physical feature associated to the object 20 located at the coordinates (φ_(i),θ_(i),d_(i))_(LCS) of the data point M_(i), as detailed below.

As illustrated on FIG. 1, non-limitative examples of objects 20 include pedestrians, trees, light posts or other vehicles. Objects 20 also include material present on the road surface such as ice, water, snow or other debris.

The object 20 may be a moving object, such as another vehicle, or a fixed object, such as a tree.

Generation of a Point Cloud Frame

To generate a continuous stream ST of point cloud frames PCF_(j), the sensor 11 comprises at least one emitter 14 and at least one receiver 15.

Advantageously, the sensor 11 comprises a single emitter 14 and a single receiver 15, preferably as a single unit, as illustrated on FIG. 3.

The emitter 14 is configured to emit a physical signal 16.

The physical signal can be a light beam, an electromagnetic wave or an acoustic wave.

The receiver 15 is configured to receive a reflected physical signal 17, corresponding to the emitted physical signal 16 once reflected in the environment E of the vehicle 1.

By “reflected”, it is understood either specular (mirror-like) or diffuse reflection.

A sensor 11 may for instance comprise a laser rangefinder such as a light detection and ranging (Lidar) module, a radar module, an ultrasonic ranging module, a sonar module, a ranging module using triangulation or any other element able to generated a point cloud frame.

Coordinates

A point cloud frame PCF_(j) corresponds to a full scan of the local volume L_(j) of the sensor 11.

By “full scan of the local volume”, it is understood that the sensor 11 has covered its complete field of view. For instance, the emitter 14 emits a physical signal that is deflected by a moving mirror rotating along two directions. After a full scan of the local volume, the moving mirror of the sensor 11 is back to its original position and ready to start a new period of rotational movement. A full scan of the local volume L_(j) by the sensor 11 is thus the three-dimensional equivalent of an image acquired by a bi-dimensional camera.

As illustrated on FIG. 1 and FIG. 2, the sensor 11 can operate a full scan by moving along two angular directions θ, φ in the local coordinate system LCS of the sensor 11.

According to this embodiment, each data point M_(i) of a point cloud frame PCF_(j) thus comprises two angular coordinates θ_(i), φ_(i).

The coordinates of a data point M_(i) in the local coordinate system LCS also comprise a radial coordinate, corresponding to the distance di from the sensor 11 to the data point M_(i) at time t_(j).

Said distance d_(i) may be computed by comparing timing of the emitted physical signal 16 and the reflected physical signal 17, for instance by comparing the time or the phases of emission and reception between the emitter 14 and the receiver 15. As an example, a time to digital converter (TDC) can measure the time of flight (TOF) of the physical signal in order to provide the distance di to the point M_(i).

Intensity Value

Each point cloud frame PCF_(j) of a continuous stream ST is generated at a given wavelength λ_(ej).

To this end, the emitter 14 of a sensor 11 can emit the physical signal in various spectral domains. The physical signal 16 can belong to the electromagnetic spectrum, such as ultraviolet, visible or infrared spectrum.

More particularly, the emitter 14 of the sensor 11 is configured to emit the physical signal 16 at a single wavelength λ_(ej) or around a single wavelength λ_(ej), for each point cloud frame PCF_(j).

By “around a single wavelength”, it is understood that although the physical signal 16 is considered to be emitted at a single wavelength, it can have a certain spectral width or range around said single wavelength λ_(ej) inherent to the emitter 14 used.

Also, the continuous stream ST can comprise a first point cloud frame PCF₁ generated at a first wavelength λ₁, a second point cloud frame PCF₂ generated at a second wavelength λ₂, a third point cloud frame PCF₃ generated at a third wavelength λ₃, etc.

According to an embodiment, the wavelengths λ_(ej) of the emitted physical signal 16 for each point cloud frame PCF_(j) can all be different or not.

According to an embodiment, the wavelengths λ_(ej) of the emitted physical signal 16 for each point cloud frame PCF_(j) can be selected in a predetermined order.

For instance, the wavelength λ_(ej) of the emitted physical signal 16 for a point cloud frame PCF_(j) can be chosen incrementally when compared with the wavelength λ_(ej−1) of the emitted physical signal 16 for the previous point cloud frame PCF_(j−1).

As a variant, the wavelengths λ_(ej) of the emitted physical signal 16 for each point cloud frame PCF_(j) can be selected in a random manner.

The receiver 15 is configured to receive the reflected physical signal 17 for each data point M_(i) of the point cloud frame PCF_(j) on a wavelength range Δλ_(r).

The wavelength range Δλ_(r) of the reflected physical signal 17 can for instance be comprised between 10 nm (nanometers) to and 250 nm.

The reflected physical signal 17 can be received over a time interval.

From the reflected signals 17 received by the receiver 15, it is possible to determine the intensity value li associated with the coordinates (φ_(i),θ_(i),d_(i))_(LCS) of each data point M_(i) of point cloud frame PCF_(j) for a physical signal 16 emitted at a given wavelength λ_(ej).

The intensity value I_(i) may correspond to the maximum amplitude of the received reflected physical signal 17 or to the attenuation of the physical signal 16 for a given wavelength. However, other calculations or measures of the intensity values are possible.

Also, the intensity value provides information on the reflectivity response at the data point M_(i) for a physical signal 16 emitted at the wavelength λ_(ej).

Since the sensor 11 is mounted on a moving vehicle 1, the environment E surrounding the vehicle 1 changes over time. A point cloud frame PCF_(j) generated by a sensor 11 at a time t_(j) comprises a full scan of a local volume L_(j) of the sensor 11 that is different from, but may overlap with, another point cloud frame PCF_(j+1) generated by the same sensor 11 at a different time t_(j+1), or generated by another sensor 11.

For instance, as illustrated on FIG. 2 and FIG. 4, coordinates (φ_(i),θ_(i),d_(i))_(LCS) of a the data point M_(i) in the local coordinate system LCS of the sensor 11 will be different when scanning a same given data point M at two different times t_(j), t_(j+1).

It is thus possible to obtain different intensity values for a same object 20 when belonging to different point cloud frames, each point cloud frame being generated with physical signals 16 emitted at different wavelengths λ_(ej).

However, one needs to ascertain the fact that the intensity values obtained with different point cloud frames correspond in fact to the same object 20.

It is thus necessary to be able to correlate the point cloud frames PCF_(j), PCF_(j+1) generated at different times t_(j), t_(j+1) by the one or several sensors 11, and to aggregate the intensity values Ii representative of the reflected signals 17 of the same object 20 for physical signals 16 emitted at different wavelengths λ_(ej).

Central processing unit

The system 10 further comprises a central processing unit 12 connected to the sensor 11 or the plurality of sensors 11.

The central processing unit 12 can be integrated inside the sensors 11 as a single unit or alternatively, can be a distinct unit secured inside a vehicle 1. In some embodiments, the central processing unit 12 may be a part of the vehicle processing unit.

The vehicle may be able to operate a self-driving or a driving assistance algorithm to drive or assist the driving of the vehicle 10, in particular by using the information provided by the system 10. To this end, the system 10 may control several actuators 4 connected to several vehicle elements 5 a, 5 b, 5 c, 5 c, such as the drivetrain, the brakes, etc.

The central processing unit 12 may communicate with the sensors 11 by wireless communication, such as radio or optic communications, or by wired communications, for instance if the central processing unit 12 and the sensor 11 are mounted on the same vehicle 1. The central processing unit 12 may communicate with the sensors 11 by using some intermediary element, in particular for long range communication.

The central processing unit 12 is configured to continuously receive the continuous stream ST from the sensor 11.

By “continuously receive”, it is understood that every time a sensor 11 has generated a new point cloud frame or a short sequence of point cloud frames, said point cloud frame or short sequence is sent to the central processing unit 12 while the vehicle 1 is moving.

The central processing unit 12 stores the continuous stream in a memory 13. The memory 13 might be integrated in the central processing unit 12.

The central processing unit 12 is configured to dynamically determine the coordinates (φ_(i),θ_(i),d_(i))_(GCS) of each data point M_(i) of a point cloud frame PCF_(j) in a global coordinate system GCS of the environment E surrounding the vehicle 1.

The global coordinate system GCS may in particular be independent of the vehicle 1 and of the movement of the vehicle 1. The global coordinate system GCS can for instance relate to an International Terrestrial Reference France (ITRF).

Alternately, the global coordinate system GCS may also be dependent on the local reference frame of the vehicle 1, for instance by being defined from the local coordinate system LCS associated to a sensor 11.

By “dynamically determine the coordinates”, it is understood that the determination of the coordinates (φ_(i),θ_(i),d_(i))_(GCS) of each data point M_(i) of a point cloud frame PCF_(j) in the global coordinate system GCS is performed while the vehicle 1 is moving, advantageously before generating the next point cloud frame by the sensor 11.

The central processing unit 12 is then configured to determine a reflectivity response 30 of the object 20 and to identify the material composition of the object 20 located in the environment E from the reflectivity response 30.

By “material composition”, it is understood the composition of the material forming the object 20 or the surface of the object 20.

Non limitative examples of material composition include metal, plastics, glass, skin, plant material, ice, snow, asphalt, cement, water etc. More generally, material composition can be of any object that is located in the environment E of the vehicle 1.

Method for Identifying Material Composition

The method for identifying material composition of objects in a 3-dimensional volume or space will now be described in more details in relation with FIG. 6.

In a first step A, a point cloud frame PCF_(j) of a continuous stream ST is generated by emitting a physical signal 16 at a given wavelength λ_(ej).

The point cloud frame PCF_(j) comprises a set of data points M_(i), in the local coordinate system LCS.

A data point M_(i) comprises coordinates (φ_(i),θ_(i),d_(i))_(LCS) of an object 20 in a local volume L_(j) at time t_(j) in a local coordinate system LCS.

The data point M_(i) also comprises an intensity value li representative of the physical signal 17 reflected on the object 20.

In a second step B, from the point cloud frame PCF_(j), the central processing unit 12 dynamically determines the coordinates (φ_(i),θ_(i),d_(i))_(GCS) of the data point M_(i) of the point cloud frame PCF_(j) in the global coordinate system GCS.

To this end, the central processing unit 12 determines an aligned point cloud frame PCF_(j,align) in the global coordinate system GCS by comparing the point cloud frame PCF_(j) with a global cumulated tridimensional map CM.

The global cumulated tridimensional map CM is also sometimes referred as a global tridimensional map, a global 3D map or a 3D map. These expressions cover the same concept and the same feature of the disclosure.

The global cumulated tridimensional map CM is a map of the environment E of the vehicle 1 in the global coordinate system GCS.

If the global cumulated tridimensional map CM of the environment does not exist yet or contain no data, the second step B comprises the operation of creating the global cumulated tridimensional map CM from the point cloud frame PCF_(j).

For instance, the point cloud frame PCF_(j) may be the first received point cloud frame PCF, from a sensor 11. A global coordinate system GCS of the environment may then for instance be defined from the local coordinate system LCS associated to the sensor 11.

Alternatively, if the global cumulated tridimensional map CM of the environment already exists and contains some data, the second step B comprises the operation of determining an aligned point cloud frame PCF_(j,align) in the global coordinate system GCS of the environment E of the vehicle.

The alignment may be performed for instance by using image registration, or Simultaneous Localization and Mapping (SLAM), such as the method disclosed in the patent document WO2018/091651.

According to this method, determining an aligned point cloud frame PCF_(j,align) is performed by comparing the generated point cloud frame PCF_(j) with the global cumulated tridimensional map CM of the environment E.

The aligned point cloud frame PCF_(j,align) may be computed only from the point clouds generated by the sensor or the plurality of sensors 11 and without additional positioning information.

By “without additional positioning information”, it is in particular meant that the computation of the aligned point cloud frame PCF_(j,align) does not require other input data than the point cloud frames generated by the sensors 11 and the global cumulated tridimensional map CM. For instance, no additional positioning or orientation element, such as a GPS or an accelerometer, is required. Moreover, no assumption has to be made on the location or movement of the sensor.

The central processing unit 12 tries to align said point cloud frame PCF_(j) so that at least a portion of the aligned point cloud frame matches at least a portion of the global cumulated tridimensional map CM.

This can be accomplished by comparing said point cloud frame PCF_(j) with the global cumulated tridimensional map CM of the environment E.

The global cumulated tridimensional map CM is then updated by merging said aligned point cloud frame PCF_(j,align) with the global cumulated tridimensional map CM.

More precisely, if the point cloud frame PCF_(j) can be aligned with at least a portion of the global cumulated tridimensional map CM of the environment E, the aligned point cloud frame PCF_(j,align) is merged with said at least one portion of the global cumulated tridimensional map CM.

From the aligned point cloud frame PCF_(j,align) in the global cumulated tridimensional map CM, the central processing unit can determine the coordinates (φ_(i),θ_(i),d_(i))_(GCS) of the data points M_(i) in the global coordinate system GCS.

In a third step C, the central processing unit 12 stores in the memory 13 the intensity value li and the coordinates (φ_(i),θ_(i),d_(i))_(GCS) of the data point M_(i) in the global coordinate system GCS.

Steps A to C are repeated with one of the sensors 11 generating a second point cloud frame of a continuous stream by emitting the physical signal 16 at a second wavelength λ_(ej+1).

More precisely, steps A to C can be repeated several times, and more particularly more than two times, so that several point cloud frames are generated by emitting the physical signal at several other wavelengths.

Some of the subsequent point cloud frames can be emitted by the same sensors or by several sensors.

Given the fact that steps A to C are repeated, at least two, and preferably a higher number of intensity values can be associated to the same object 20 in the global coordinate system GCS.

If the point cloud frames are emitted by several sensors, the wavelengths of the corresponding emitted physical signals can belong to different spectral domains, which can be useful to acquire intensity values for various types of physical signals (infrared, visible light, ultraviolet, etc.).

Also, in a step D, the central processing unit 12 determines the reflectivity response 30 of the object 20 from the intensity values acquired for the object 20 with each point cloud frame PCF_(j).

As illustrated on FIG. 5, the reflectivity response 30 is obtained by aggregating the intensity values I acquired at several different wavelengths λ_(ej).

More precisely, in the example of the FIG. 5, the reflectivity response 30 is obtained from the reflected physical signals 17 ₁, 17 ₂, 17 ₃, 17 ₄, 17 ₅ corresponding to physical signals emitted at several different wavelengths λ_(e1), λ_(e2), λ_(e3), λ_(e4), λ_(e5) once reflected on the object 20. From this reflected physical signals 17 ₁, 17 ₂, 17 ₃, 17 ₄, 17 ₅, intensity values I₁, I₂, I₃, I₄, I₅, such as the maximum amplitude value, can be obtained.

In a step E, the central processing unit 12 identifies the material composition of the object 20.

In this step E, the reflectivity response 30 can then be compared with reference reflectivity responses of known materials stored in a library. The library can be stored in the memory 13 of the central processing unit 12.

Advantages

Thanks to the above, it is possible to obtain the composition material of an object 20 although the vehicle 1 is moving relative to the object 20 during the implementation of the method. This allows time-multiplexed, real time and efficient processing of the reflection of multispectral physical signals.

The method can be implemented even though the relative positions and orientations between the sensors are unknown.

The vehicle 1 can implement the method in any known driving conditions, for instance during daytime or night-time, in various weather conditions, in various road conditions, etc.

As stated above, the timeframe of a point cloud frames is determined and/or managed by the central processing unit 12. This way, there is no need to communicate with a remote server for instance that would be located outside of the vehicle 1.

Besides, the successive physical signals emitted by the sensor 11 for the respective point cloud frames can be selected randomly.

A random selection permits to prevent any interference with other physical signals 16 that could be emitted by other vehicles or devices in the environment E. The system 10 is thus safer and robust against fake signals that could undermine the security and integrity of the vehicle for instance.

As a variant, the successive physical signal 16 emitted by the sensor 11 for the respective point cloud frames can be selected in a predetermined order.

For instance, the wavelength of the emitted physical signal 16 for a point cloud frame can depend on the reflected physical signal 17 acquired for a previous point cloud frame. As an example, if the reflected response 17 acquired for the previous point cloud frame is characteristic of an object either made of paper or fabric, the wavelength of the emitted physical signal 16 for the point cloud frame should be selected so as to discriminate specifically between these two materials.

More generally, the wavelengths of the successive emitted signals 16 can be selected so as to converge toward a probability threshold above which material composition of the object 20 is considered to be determined. Such convergence can be implemented by using any classification method, such as a decision tree.

As will be well understood by those skilled in the art, the several and various steps and processes discussed herein to describe the disclosure may be referring to operations performed by a computer, a processor or other electronic calculating element that manipulate and/or transform data using electrical phenomenon. Those computers and electronic elements may employ various volatile and/or non-volatile memories including non-transitory computer-readable medium with an executable program stored thereon including various code or executable instructions able to be performed by the computer or processor, where the memory and/or computer-readable medium may include all forms and types of memory and other computer-readable media.

The foregoing discussion disclosed and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims. 

What is claimed is:
 1. A method for identifying a composition material of an object located in an environment surrounding at least one device, in which at least one sensor is mounted on the device and communicates with at least one central processing unit, wherein: /A/ the sensor generates a point cloud frame of a continuous stream by emitting a physical signal at a wavelength, wherein the point cloud frame comprises a set of data points, at least one data point comprising coordinates of the object in a local volume surrounding the sensor at time t_(j) in a local coordinate system of the sensor, said data point also comprising an intensity value of a reflected physical signal corresponding to the emitted physical signal once reflected on the object, /B/ the central processing unit receives the point cloud frame and determines the coordinates of each data point of the point cloud frame in a global coordinate system of the environment surrounding the device, the intensity value being associated with the coordinates of each data point in the global coordinate system, /C/ the central processing unit stores in a memory the coordinates of the object in the global coordinate system, steps /A/ to /C/ are repeated with the sensor or another sensor generating another point cloud frame by emitting another physical signal at another wavelength, so that at least two intensity values are associated to coordinates of the object in the global coordinate system, /D/ the central processing unit determines a reflectivity response of the object from the at least two intensity values, and /E/ the central processing unit identifies the composition material of the object.
 2. Method according to claim 1, wherein the central processing unit determines the coordinates of each data point of the point cloud frame in the global coordinate system of the environment surrounding the device by: comparing the point cloud frame with a global cumulated tridimensional map of the environment to determine an aligned point cloud frame in the global coordinate system, and updating the global cumulated tridimensional map by merging the aligned point cloud frame with the global cumulated tridimensional map.
 3. The method according to claim 1, wherein the sensor comprises at least one emitter and at least one receiver, the emitter being configured to emit a physical signal and the receiver being configured to receive the emitted physical signal once reflected on the object.
 4. The method according to claim 3, wherein the sensor comprises the emitter and the receiver as a single unit.
 5. The method according to claim 1, wherein the central processing unit identifies the composition material of the object by comparing the reflectivity response determined at step /D/ with reference reflectivity responses of known materials stored in a library.
 6. The method according to claim 1, wherein the wavelengths of the physical signals emitted for the point cloud frames are selected in a random manner.
 7. The method according to claim 1, wherein the wavelengths of the physical signals emitted for the point cloud frames are selected in a predetermined order.
 8. The method according to claim 1, wherein the device comprises a plurality of sensors, wherein the sensors can respectively generate a point cloud frame by emitting a physical signal at a wavelength comprised in different spectral domains.
 9. The method according to claim 8, wherein the sensors all communicate wirelessly with the central processing unit.
 10. The method according to claim 1, wherein a point cloud frame (PCF_(j)) corresponds to a full scan of the local volume of the sensor.
 11. The method according to claim 1, wherein the coordinates of the object in the local coordinate system of the sensor comprises two angular coordinates and one radial coordinate.
 12. The method according to claim 11, wherein the radial coordinate corresponds to the distance from the sensor to the data point (Mi), the distance being computed by comparing timing of the emitted physical signal and the reflected physical signal.
 13. The method according to claim 1, wherein steps /A/ to /C/ are repeated at least four times, so that at least four intensity values are associated to coordinates of the object in the global coordinate system.
 14. The method according to claim 1, wherein the physical signal is a laser signal.
 15. The method according to claim 1, wherein the device is a vehicle able to move in the environment.
 16. A system for identifying the composition material of an object located in an environment surrounding at least one device, the system comprising: a plurality of sensors configured to be mounted on said at least one device, each sensor being configured to generate a continuous stream of point cloud frames, in parallel and asynchronously with the other sensors, by emitting a physical signal at a wavelength, wherein the point cloud frame comprises a set of data points, each data point comprising coordinates of the object in a local volume of the environment surrounding the sensor at time t_(j) in a local coordinate system of the sensor, each data point also comprising an intensity value of a reflected physical signal corresponding to the emitted physical signal once reflected on the object, a central processing unit configured to communicate with each sensor to continuously receive the continuous streams from the sensors, determine the coordinates of each data point of the point cloud frame in a global coordinate system of the environment surrounding the device, and store in a memory the intensity value and the coordinates in the global coordinate system, the central processing unit being configured to determine a reflectivity response of the object from the intensity values and to identify the composition material of the object.
 17. An autonomous or semi-autonomous vehicle comprising a system according to claim
 16. 18. A non-transitory computer readable storage medium, having stored thereon a computer program comprising program instructions, the computer program being loadable into a central processing unit of a system according to claim 16 and configured to cause the central processing unit to carry out the steps of a method according to claim 1, when the computer program is run by the central processing unit. 